Low flow of axial piston pump

A pump supplying seal high pressure seal oil to a compressor with floating oil seals was disassembled for maintenance due to low flow problem. This is an axial piston pump with a barrel housing seven plungers. The barrel is surrounded by a bearing and housed in a casing. A splined shaft is responsible for the rotation of the barrel in the casing.

The seal oil bottle low level alarm sounded several times and the standby pump had to be taken in service. Whenever the standby pump was shutdown the low level alarm sounded which indicated low flow of seal oil pump. The pump was removed and taken to workshop for overhauling. On dismantling, it was observed that the clearance between the plungers and the housing had increased from 0.05 mm to 0.10 ~ 0.15 mm in all plungers.

In reciprocating pumps, minor changes in clearances can result in high effects to efficiency. The plungers and the barrel were replaced with new ones and pump was assembled. The pump was installed in the area and is now giving appropriate flow.

Modification of Pump Mechanical seal

We have a urea solution pump used for recovery of urea dust. Due to discontinuous and frequent start ups and shutdowns of the pump, the mechanical seal had a history of failures after every two to three months. The mechanical seal of the pump had to be attended every alternate month which caused lots of man hours and cost the company heavy consumption of inventory.
After some research it was decided to replace the existing mechanical seal with gland packing. This was done such that no machining of pump was required so as to revert back to the original design if necessary. The original seal design is shown below

The seal was modified with a spacer and a gland plate such that the gland plate was the size of the mechanical seal and a flushing line was provided for the packing. The modified seal arrangement is shown below